Method of making resistance elements



Nov. 17, 1936. V N. c. SCHELLENGER 2,061,107

'METHOD OF MAKING RESISTANCE ELEMENTS Filed Nov. 2, 1934 2 Sheets-Sheet 1 FEB CENT EOTHT/OM 1r 5 1 J'NVENTOR.

N5 wTaN (BELLE/VGA)? Ea: EY 1 1936- N. c. SCHELLENGER ,1

METHOD OF MAKING RESISTANCE ELEMENTS Filed Nov. 2, 1934 2 Sheets-Sheet 2 INVEN TOR. NEWTUN C. ScHELLENsm.

Patented Nov. 17, 1936 UNITED STATES PATENT OFFICE METHOD OF MAKING RESISTANCE ELEMENTS Newton 0. Schellenger, Elkhart, Ind., assignor to Chicago Telephone Supply 00., Elkhart, Ind., a

corporation of Indiana Application November 2, 1934, Serial No. 751,192

4 Claims. (Cl. iii-es) My invention relates to resistance elements For the most part, resistance elements of this and to the manufacture thereof, and moreparticularly to resistance elements of the planar carbonaceous type.

This application is a continuation in part of intersperse increments or particles of the'abutting edges of adjacent areas in'an effort to efiect coalescence therebetween, to reconcile the difference in their specific resistances. However, this 55 has not proved successful,

type were made by painting, or by electro-chemical deposition, and it is largely due to these methods of manufacture (which do not lend themselves to delicacy of control nor fineness of apat the center of, though obliquely disposed to, the

plane of said fiat surface.

Fig. 4 is a diagrammatic composite view illustrating the pattern created upon a flat surface by my spray which is partially intercepted by 5 5 my co-pending application Serial No. 666,444, plication) that the several coatings of composfiled April 17, 1933, for Resistance element. ite elements have not been more gradually In variable resistance devices, or volume conblended to secure less angular gradient curves. trols, which for the sake of convenience will In my prior Patent No. 1,771,236, I disclose a hereinafter be referred to as rheostats, it is means of manufacturing a composite resistance 10 frequently desirable to have a resistance eleelement of thetype hereinbefore discussed, ment, which is composed of a plurality of areas where it is necessary to have the rate of resistof conductive materials, each of a diflerent speance-increase constant through one range of cific resistivity than the others. The purpose movement of the contactor, and where, through for this is well known to be the demand in the another range, the rate of increase, although 15 radio art for rheostats in which the change of constant, is much more rapid than the first the effective resistance is not directly proporrange. However, in such disclosure it is only tional to the degree of movement of the conpossible to join the different sections abruptly, tactor over the contact surface of the resistance despite the desirability of having a gradual element. The rate of change of ,eifective remergence thereof. 20 sistance, relative to the actual movement of the Therefore, it is an object of the present incontactor, may be several thousand times greater vention to provide a resistance element of the in some portions of the resistance element than p a a a o aceo C mp resistance t p in others, tosecure smooth control and evenness having its various sections of difiering resistivof reproduction in certain types of radio sets. ities gradually merged to secure a regular, unl- 25 The demand .for these composite resistance form resistance gradien. elements has heretofore been satisfied with ele- It is another object of my invention to pro- .ments made by disposing upon a suitable base, vide a novel method for making such an elein abutting relation, various areas of conductive 1 me t w e by ac u acy a evenness of coatings material; each of a different specific resistivity. is assured and whereby a perfe gradual 30 So long as the contactor moves within the congence between coatings is attained. finesof-any one of these areas, the increase or Other'objects of my invention will become apdiminution of eifective resistance, (depending on parent upon consideration of the following specithe direction of movement), is regular and fication when taken in conjunction with the smooth. However, when the contactor passes following drawings, in which: 35

from .an area havingone specific resistivity, to an Fig. 1 is a diagrammatic vertical sectional .view dj th rea, of another. specific resistivity, taken along the longitudinal axis of a resistance th .1 n bru t change in resistance, which element made in accordance with my invention,

I causes a sharp, angular departure in the rein which the component parts of the element have 1'4 sistance gradient of the element. been drawn in grossly exaggerated. proportion; 40 nsindicated above, some of the contiguous the element being Projected upon a ap to areas of th r si t nc 1e nt difier so widely illustrate the resistance-length curve thereof. r elative to their respective specific resistivities, Fig. 2 is a diagrammatic composite view ilthat an abrupt change of. resistancefollows when lustrating the pa ed up a flat sur- "i the contactor passes therebetween,.which mateface by a spray formed in accordance with my ,rially and adverselyaffects reproduction. invention having its longitudinal axis perpen- There have beenefiort's made to overcome this dicular to the plane of the flat surface. difficulty which have been only partially suc- Fig. 3 is a diagrammatic composite view illuscessful, and which have fallen far short of pertrating the pattern created upon a fiat surface fection. The most common practice has been to by my spray having its longitudinal axis directed 50 the flat surface while disposed at a degree of inclination thereto.

Fig. 5 is a diagrammatic elevational view of my nozzle and spray, illustrated with the nozzle in section.

Fig. 5a is a plan view of a pattern created on a flat surface by the spray shown in Fig. 5.

Fig. 6 is a diagrammatic view of my nozzle and spray, showing the effect of thespray upon differently inclined surfaces.

Fig. '7 is a diagrammatic view of two sprays angularly disposed upon opooosite sides of a moving strip.

Figs. 8, 9, and 10 are exaggerated sectional views taken along lines 8-8, 9-9 and Ill-Ill, respectively, of Fig. 5.

Fig. 11 is a diagrammatic perspective view of an angularly inclined, moving strip passing before a horizontally disposed spray station, where it 'is receiving a transversely graduated coating in accordance with this invention.

Fig. 12 is a plan view of a blank prepared in accordance with my invention illustrating how a variety of resistance elements mav be stamped therefrom, whereby each will have a different resistance gradient.

Fig. 13 represents a microscopic plan view of the contact surface of a composite resistance element made in accordance with my invention, illustrating the interspersion of particles of an overlying coating upon an underlying coating at their point of mergence.

Whereas, for purposes of illustration it has been necessary to show the conductive coatings of the resistance elements described herein as being of substantial thickness, it must be realized that such coatings are frequently only two to three thousandths of an inch in thickness, and but rarely. exceed eight thousandths of an inch. Likewise, hereinafter where it has been necessary to refer to the mergence of adjacent coatings as taper or tapering of one such coating upon another, the taper refers not so much to an actual gradual diminution in thickness of the top coating, but rather to a lateral, progressively increased spacing between the particles of the top coating upon the bottom coating, whereby a gradual blending of the superficial areas of the adjacent coatings is effected.

Referring more specifically to the drawings in which like reference characters refer to like parts throughout:

In Fig. 1, l represents a suitable base or bodyportion which serves as amounting for the conductive coatings 2, 3, 4 and 4a. The. base may be either of conductive or insulatory material, and has applied to one of its surfaces, an overall coating 2, of any desired resistance value.

Superimposed upon this coating are other coatings 3, 4 and 4a; each having a specific resistivity of the value necessary, when combined with the others, to create a resistance element having an overall resistance of any desired predetermined characteristics.

An arbitrary representation of a resistance gradient has been illustrated on the graph of Fig. 1 to show the effects of this invention when employed in the manufacture of a resistance element, as the one shown therein. The overall coating 2 is sprayed on in the manner shown in Fig. 2 whereby a coating of substantially uni-, form thickness is provided over the base I. The coating 3. is sprayed over the coating 2 in a manner similar to that shown in Figs. 4 and 11 whereby a tapering effect is obtained. T fifi, t0

.. tapered coating is In Fig. 5, I have diagrammatically represented a nozzle in vertical section each end of the element thus formed is sprayed low resistance paint 4, 4a, each, likewise, tapering to gradually merge with their respective underlying coatings, 3 and 2.

The effect of tapering these coatings is apparent in the graph: The low resistance paint 4 throughout its portions of uniform density produces a slow gradation of the curve. Its tapering out upon the coating 3 causes a diminution of its short-circuiting effect, and gives rise to a gradual increase of resistance. The line of demarcation between coatings 3 and 4. is imperceptible due to the gradual tapering-off of coating '4, nor is there any perceptible abrupt increase in the resistance gradiant at this junction by virtue of the delicate gradation.

This gradual curve or elbow is represented on the graph between the projection lines A and B extending from the limits of the taper. Coating 3 gives a gradual increase of resistance at a definite rate, until the contactor traverses the taper thereof, which, as in the case of coating 4, causes the elbow shown between projection lines C and D on the graph. The overall coating 2, being of a greater specific resistance than coating 3, gives a greater increase in resistance for a given movement of the contactor, than does coating 2; and as suggested above, the difference in their resistance values is reconciled by the ta per of coating 3. The low resistance paint 4a is applied so that a gradual short-circuiting may be achieved as represented upon the graph.

Resistance elements having the general characteristics of the one above described may be made by passing a strip or web I of suitable base material, such as heavy paper, past one or more nozzles N, according to the type of element desired, to receive a spray therefrom.

In my prior patent above referred to, I have disclosed various forms of conductive material which are suitable for this purpose. A mixture of different forms of carbon in a shellac solution may be employed, wherein the resistance char acteristics of the mixture can be varied by changing the portions of conductive and non-conductive ingredients relative to each other.

The coatings may be applied uniformly over the entire web by positioning the nozzle centrally and perpendicularly thereover, as shown in Fig. 2, or they may be applied to taper in thickness across the web, as is shown in Fig. 3, by positionprovide the web with a tapering coating which extends but partially across the surface thereof. This is likewise illustrated in Fig. 11.

The tapering effect of the spray may be augLjQ, mented by employing a nozzle of certain con-- web I are positioned relative to eachother to struction, whereby the function of inclining thef,

spray and web relative to each other to obtain. a

supplemented.

to illustrate the spray action referred to. The coating material is forced through the central jet 5 of the nozzle N. Compressed air is released through the passage 6, which is concentrically arranged about the jet 5, to atomize the coating material at the nozzle orifice I. The nozzle imparts a swirling motion to the compressed air, whereby the outer portions of the. stream being emitted from the jet 5 are more completely atomized' or aerated than the more central portionsof the stream. Thus, the

central portion 8 of the spray is of greater density than its outer portions, 9.

Fig. 5a diagrammatically illustrates the pattern created by a spray when the nozzle is perpendicularly positioned over the web. Observe the comparatively uniform dense center 8' and the highly difi'used peripheral portions 9' of the pattern. I

To obtain the most uniform coating of maximum density, the web I should be perpendicularly positioned relative to the spray to intercept only the central portion 8 thereof, whereby the less dense and tapering portions 9 of the spray are not used. (See Fig. 6.) If the web is positioned as shown in dotted lines in this figure, the taper of the coating, as discussed in connection with Fig.4, will be appreciably increased. That portion of the web intercepting the spray at its center, which is in closest proximity to the nozzle, will receive the densest coating. The webs inclination away from the nozzle combined with the less dense portions 9 of the spray cause a rapid diminution in the coating to effect a marked taper thereof.

Where it is deemed desirable to overlap coatings, two or more nozzles, as N:--N2 of Fig. 7, may be positioned to spray the web from its opposite sides to project sprays at an angle to the plane of the web. These nozzles are positioned in order that their sprays may play upon the moving web I, so that their portions of less intensity, i. e., those portions playing upon the remoter portions of the web, fall in the same path on the web. Thus, the tapering portion of the coating thus formed applied by the spray of nozzle N1, is overlapped by the tapering portion of the coating applied by the spray of nozzle N2. In this manner a composite resistance element is formed, having a perfectly uniform contact surface, and smoothly graduated resistance characteristics. This may be better understood by referring to Figs. 8, 9 and 10 which represent sectional views of the web I shown in Fig. 7. These views have been greatly enlarged and exaggerated for purposes of illustration.

So far as I am aware, the only successful way of achieving these results is by depositing the conductive material upon ,the web by means of spraying, since no other method of deposition permits of such fine, controllable distribution and interspersion.

This will become more obvious from the inspec tion of Fig. 13. Here I have diagrammatically illustrated a microscopic view of a portion of my resistance element in order that I may more clearly point out the differences between composite elements made by spraying, as shown and described herein, and other well known methods of coating.

In Fig. 13, I have illustrated an overall coating, corresponding to the coating 2 of Fig. l, by white particles 2', with a coating, corresponding to the coating 3 of Fig. 1, superimposed thereon, represented by the dark particles 3. The view of Fig. 13 is taken at the point where the coating 3 tapers away to the coating 2.

-' By virtue of,a spray being operated and controlled as -has hereinbefore been discussed, the particles 3 of the dark coating are massed closely together to form a solid coating 3 over the coating 2, and gradually taper out upon coating 2. This solid coating 3 has a uniform rate of resistance increase throughout its length, and as was mentioned in connection with Fig. 1, the'coating 2, has a different, though uniform resistance increase throughout its length.

The densely massed particles 3' of the coating 3 were deposited by disposing that portion of the element upon which they rest closest to the spray gun. The portions of the element more remote from the spray gun received the particles in less compact relation. Thus, the density of the coating is inversely proportional as the distance from the spray gun. Hence, the particles 3' become scattered and more sparsely settled whereby more and more of the particles 2 appear at the surface.

For any unit area, the resistance is equalto the combined resistances of the particles; varying in the proportion that the dark particles 3' vary to the light particles 2'. Virtually, coalescence is effected between the coatings.

In all other methods of coating, there necessarily is a well defined line of demarcation between the coatings. Obviously there cannot be such an interspersion of particles when the coating material is applied with a brush or by electro-chemical deposition.

I have illustrated and described but a limited application of my invention. Nevertheless, I contemplate that any coating or combinationofcoatings, either conductive, insulatory or both, may

be applied by my novel method to secure a resistance element having the desired characteristics.

Referring now to Fig. 12, the base I, after having received a suitable coating or plurality of coatings, may have stamped therefrom arcuate or elongated pieces. These pieces constitute the resistance elements, and, of course, may be stamped out in any desired shape. By way of example, Ihave designated the arcuate elements with an X, and the elongated straight elements with a Y. It will be noticed that the elements X are illustrated in various positions; i. e., their end portions fall in difierent relative positions upon the web. In this manner resistance elements having diiferent resistance gradients may be made from the same stock, whereby a greater range of demand may be satisfied. The strips Y may be cut transversely, longitudinally or obliquely from the web for the reasons recited above.

, I have illustrated the web passing beneath or past stationary spray stations, but, of course, the web may be fixed, and the spray guns may be moved relative thereto to effect the same result.

Likewise, any suitable manner of forming a spray which varies in intensity to provide a tapering coating, as by forming the spray nozzle orifice in any suitable way, is within the contemplation of this invention.

I claim as my invention:

1. The process of forming a resistance element having a plurality of resistance sections charac- 4 a thereon, and-directing a spray of coatingcomposition at an acute angle to a median planeof the base. to deposit a second conductive layer overlyinga p'ortio'nof said' first' conductive layer, said second layer having a-tapered edge.

3. The process oi forming a resistance element havinga plurality of adjacent sections of differer t specific. resistivitie's with a smooth taper in resistivityibetween adjacent sections which comprises, depositing a layer of coating material on a base; and spraying on said base, over a portion ofsaid layer, a coating material having a different specific resistivity than the first-named coat- "'mg material, said spray being positioned with 15 respect to said base to provide a smooth taper in thicimess of material at a lateral boundary of saidsecond layer.

4. The process of forming resistance elements having sections of different specific resistivities,

which comprises, depositing a conductive coatin on a base to form a section having a predetermined specific resistivity, and directing at an acute anglev to the plane of saidcoating. a spray of conductive coating material to form a section overlying a portion of said first coating and having a different specific resistivity than said first section, the transverse juncture of said sections having a tapering specific resistivity.

NEWTON C. SCHEILENGER. 

